A grand jury in North Carolina on Monday indicted a 17-year-old girl on suspicion of aiding and abetting the May 18 shooting that killed three people at a mosque in San Diego by recording and disseminating a live video of the attack.

Forsyth County District Attorney Jim O’Neill told a press conference that officials decided to bring state charges because in North Carolina the girl can be tried as an adult. She faces a potential sentence of life in prison without parole if convicted in North Carolina, while federal charges could result in a three- or four-year sentence.

The three men who died in the attack were credited with thwarting more violence at a time when 140 children were at the mosque’s school. The victims, security guard Amin Abdullah, 51, caretaker Mansour Kaziha, 78, and Nadir Awad, 57, the husband of a teacher at the Islamic Centre of San Diego, were hailed as heroes at a memorial service.

The assailants, Caleb Vazquez, 18, and Cain Clark, 17, killed themselves in their vehicle upon fleeing the scene. Investigators say they also intended to attack a Jewish temple and a predominantly African American high school.

Read: ‘I saw bad stuff’, says 9-year-old who huddled in closet during California mosque attack

Sarah Lindsey Santiago was arrested last week. The indictment returned on Monday accused her of three counts of murder and one count of conspiracy.

Reuters could not identify any attorney for Santiago.

O’Neill said a person may be guilty of aiding and abetting if he or she shares the same criminal intent as the perpetrator and fails to render aid during the crime, even if not physically present.

Before the attack, Santiago agreed to livestream it, disseminate the recording publicly and then release the manifesto authored by the attackers to justify the attack, O’Neill’s office said in a press release.

O’Neill described the suspects as part of an “underground subculture” that radicalises people to commit horrific crimes.

Read more: Over 2,000 gather in San Diego to mourn three men killed in mosque attack

“It’s an echo chamber of intense hate against different cultures and religions. Cain and Vazquez, by what is contained in their manifesto, seem to hate everyone, regardless of skin colour, politics, religion, or ethnicity, and this underground subculture of hate – they listen to each other, they talk to each other in encoded platforms,” O’Neill said.

Investigators determined that three people watched a livestream of the attack, O’Neill said. At first they only knew one of them was a woman in the Eastern time zone, but later were able to identify Santiago. He declined to say whether the other two people who were watching were also identified or whether they too would face charges.